Mechanistic modeling of cutting forces and tool flank wear in the thermally enhanced turning of hardened steel

Thermally enhanced machining (TEM) is a method to improve the machinability of hard materials. In the literature, few investigations focus on the analytical modeling of machinability characteristics in the TEM. For this reason, this research tries to present theoretical models to better understanding of cutting forces and flank wear in the TEM process. The goal of this study is to present a methodology for predicting cutting forces and tool flank wear during thermally enhanced turning of hardened steel AISI 4140. A mechanistic model is developed to estimate the cutting forces under different TEM conditions by considering shear stresses in the primary and secondary shear zones as well as applied forces on the tool edge. A flank wear model is developed to estimate abrasion, adhesion, and diffusion wears by attention to some considerations such as the effect of TEM on the reduction of material hardness, thrust force, and the effect of multi-layer coated carbide tools on flank wear. Comprehensive experimental results are classified into two groups for calibration as well as verification of analytical models. By precise application of external concentrated heat source, the temperature in the shear plane and frictional area increases which finally leads to reduction of cutting forces. In other words, rising of uncut chip about 300 °C results in decreasing of shear stress in the frictional area about 200 MPa. Abrasive and adhesive were the dominant wear type in high levels of cutting speed and uncut chip temperature, respectively. The effect of cutting speed decreased in high value of uncut chip thickness due to the reduction of particle hardness in comparing with the hardness of tool coating.